The invention disclosed herein relates generally to ultrasonic sensors, and more specifically to single transducer, pulse transmission ultrasonic range finders with enhanced noise rejection capabilities.
It is well-known to detect the presence of and/or determine the distance to a target object by transmitting acoustic energy toward the object, receiving reflections of the transmitted acoustic energy from the object and computing distance based on round trip travel time and the propogation speed of the acoustic energy. Sensors employing this approach are being used to an increasing extent in a variety of industrial and other applications. Some characteristics which make acoustic sensors particularly desirable in industrial settings are ability to sense presence without physical contact, relative insensitivity to dust, smoke, moisture and other contaminants in the target area, and minimum likelihood of contributing to explosions in explosive environments.
However, it is also well-known that industrial settings provide particularly severe acoustic noise conditions for operation of acoustic sensors. There may be high noise intensities and large variations in both intensity and frequency content, depending on the application and setting. Since the distance sensing ability of a pulse transmission acoustic sensor is dependent on accurate detection of the arrival time of an echo, the sensor must be able to reject environmental noise which distorts the received echo.
A variety of methods and apparatus have been used to improve the ability of acoustic sensors to operate reliably under acoustically noisy conditions. These include various types of filters and filtering techniques and a number of other approaches to the problem. For example, U.S. Pat. No. 3,454,922 issued to J. Dory on July 8, 1969 discloses ultrasonic pulse distance measuring device in which a peak detector and a threshold unit are used to accurately determine time of arrival of the leading edge of an echo pulse. Operation under noisy conditions can also be improved by establishing a detection window around the expected arrival time of an echo pulse.
The applicants have devised a single transducer, pulse transmission, ultrasonic sensor employing a unique method and arrangement of components for achieving enhanced ability to operate reliably in acoustically noisy environments. The sensor is of a relatively simple, compact design and is capable of good distance sensing accuracy and operational flexibility.